Coffee beverages are one of the most popular and universal drinks in the world. One popular type of a coffee beverage, espresso, is brewed by forcing hot water, under pressure, through compacted coffee grounds over a short period of time. Generally, this is accomplished with an apparatus involving water tanks and plumbing, water heating elements, electric motors, pumps, valves, and filters. As a result, standard devices are usually large, expensive, and complicated, and require a skilled operator. Because of these factors, brewing a truly great cup of espresso is inconvenient and restricted to appropriate venues.
The first type of espresso machines were steam-driven machines and they were invented at the turn of the 20th Century by Pavone. A steam-driven espresso machine works by forcing water through the coffee by using steam or steam pressure. This design is still in use in lower-cost consumer kitchen appliance espresso makers. The stem-driven espresso machine is low cost because it has few moving parts. However, due to the inherent high temperature and low pressure of these devices the beverage produced is of low quality.
In the mid 20th Century Achille Gaggia, developed the first piston driven espresso machine. Generally, the piston driven espresso machine uses a lever, pulled by the operator, to pressurize hot water and send it through the coffee grinds. The act of producing a shot of espresso is colloquially referred to as pulling a shot, because of the lever-style espresso machines required pulling a long handle to produce a shot of espresso. There are two types of lever machines: direct lever and spring loaded. With the direct lever, the operator directly pushes the piston with the force of the lever. In the spring piston design, the operator works to tension a spring, which drives the piston, which then delivers the pressure needed to produce the espresso. The lever espresso machine allowed the user to finally apply the optimal pressure of 8 to 10 bars to the system.
In the 1960's espresso machines with automatic pumps were developed. The pump is typically an electric motor driven pump. This electric pump driven espresso machine remains the most popular type of espresso machine.
More recently, the air pressure espresso machine was invented. The air pressure espresso machine uses compressed air to force the hot water through the coffee grounds. The hot water is typically added from a kettle or a thermo flask. The compressed air comes from either a hand-pump, Nitrous (NO2) or Carbon Dioxide (CO2) cartridge, or an electric compressor. One of the advantages of the air pressure driven machines is that they are often handheld and portable. Unfortunately, a significant drawback to the air pressure machine is that the pressure profile is inconsistent throughout the brewing cycle, being higher at the beginning and lower at the end. A further drawback of the gas cylinder powered NO2/CO2 machines is the requirement to replenish gas cartridges because one cartridge only makes a few shots of espresso.
The present invention is generally related to a piston driven espresso machine. One example of a piston driven espresso machine is disclosed by U.S. Pat. No. 2,898,844, issued to Gaggia. The Gaggia patent discloses an automatic version of the hand lever piston driven espresso machine that Gaggia is also credited with inventing. The Gaggia espresso machines use a single large piston that is actuated when the user pulls a lever (or presses a button, in the case of the automatic machine). The single Gaggia piston pressurizes the water and forces it through the compacted coffee grounds. Although the Gaggia hand lever espresso machine has been around since the 1930's, very little, besides making it automatic, has been done to improve the machine. Indeed, the Gaggia hand lever espresso machine is still commercially available. Importantly, not every person that wants a hand lever pressed cup of espresso has the strength or body mass to provide the necessary force on the lever to bring the hot water to 8-10 bars. Furthermore, need for mechanical advantage requires a large lever securely anchored and thus results in a physically large machine. Merely finding room for the machine on a stable platform is a challenge. Additionally, the automatic piston espresso machines require a source of alternating current electricity and are therefore, not portable. Thus, what is needed is an improved portable manual espresso machine that allows even a weak user to brew a cup of espresso at the optimal 8-10 bars of pressure.